ZyXEL Communications ZyWall USG20-VPN User Manual page 145

compose the network address. The prefix length is written as "/x" where x is a number. For
example,
2001:db8:1a2b:15::1a2f:0/32
means that the first 32 bits (2001:db8) from the left is the network prefix.
Link-local Address
A link-local address uniquely identifies a device on the local network (the LAN). It is similar to a
"private IP address" in IPv4. You can have the same link-local address on multiple interfaces on a
device. A link-local unicast address has a predefined prefix of fe80::/10. The link-local unicast
address format is as follows.
Table 62 Link-local Unicast Address Format
1111 1110 10 0
10 bits 54 bits
Subnet Masking
Both an IPv6 address and IPv6 subnet mask compose of 128-bit binary digits, which are divided
into eight 16-bit blocks and written in hexadecimal notation. Hexadecimal uses four bits for each
character (1 ~ 10, A ~ F). Each block's 16 bits are then represented by four hexadecimal
characters. For example, FFFF:FFFF:FFFF:FFFF:FC00:0000:0000:0000.
Stateless Autoconfiguration
With stateless autoconfiguration in IPv6, addresses can be uniquely and automatically generated.
Unlike DHCPv6 (Dynamic Host Configuration Protocol version six) which is used in IPv6 stateful
autoconfiguration, the owner and status of addresses don't need to be maintained by a DHCP
server. Every IPv6 device is able to generate its own and unique IP address automatically when
IPv6 is initiated on its interface. It combines the prefix and the interface ID (generated from its own
Ethernet MAC address) to form a complete IPv6 address.
When IPv6 is enabled on a device, its interface automatically generates a link-local address
(beginning with fe80).
When the USG's WAN interface is connected to an ISP with a router and the USG is set to
automatically obtain an IPv6 network prefix from the router for the interface, it generates another
address which combines its interface ID and global and subnet information advertised from the
router. (In IPv6, all network interfaces can be associated with several addresses.) This is a routable
global IP address.
Prefix Delegation
Prefix delegation enables an IPv6 router (the USG) to use the IPv6 prefix (network address)
received from the ISP (or a connected uplink router) for its LAN. The USG uses the received IPv6
prefix (for example, 2001:db2::/48) to generate its LAN IP address. Through sending Router
Advertisements (RAs) regularly by multicast, the router passes the IPv6 prefix information to its
LAN hosts. The hosts then can use the prefix to generate their IPv6 addresses.
Chapter 9 Interfaces
Interface ID
64 bits
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